Telecommunication switches located within service provider facilities are used to switch communication data packets from one communication link, e.g., fiber optic cable, to another. Such a series of switches allows the data comprising the phone call or data session to be switched through the communication network to a destination. Due to physical limitations within the service provider facilities, the switch sizes, i.e., footprint, is limited. A switch typically includes a number of interface cards electrically interconnected with switch cards, also referred to as a “switch fabric card.” The electrical or fiber optic cables are terminated and driven by the interface cards, while the switch fabric cards switch the data packets from one interface card to another.
To provide interconnection and also allow the removal and replacement of interface and switch fabric cards, interface and switch fabric cards are often connected through a “backplane.” This arrangement allows the interconnection of the many cards over short distances on a high density platform. The faceplates of interface cards typically allow external connections and should permit connection or termination of multiple cables as well as a way to dress those cables without effecting maintenance to adjacent working cards. Similarly, the faceplates of switch fabric cards should allow termination of multiple cables that interconnect with adjacent systems and allow opportunity for switch fabric expandability.
Due to the high frequencies involved, the signal path distance between interface and switch fabric cards should be as short as possible to minimize degradation of the signal. To minimize signal degradation, several interface and switch fabric cards are interconnected in close proximity on the backplane. Because of the substantial cost of a backplane and small footprint availability at the service provider facilities, electronics racks are designed to connect as many circuit cards as possible through a single backplane. Interface and switch fabric cards on a back plane are typically arranged in sets of parallel, closely spaced rows of cards, with only small spaces between them.
Interface and switch fabric cards, referred to collectively herein as “circuit cards,” are substantially planar and populated with electronic circuitry and components. Circuit cards typically consume considerable power and therefore generate a substantial amount of waste heat during operation. For example, it is not uncommon for circuit cards to consume 700 Watts of power each. To prevent damage to the sensitive electronic circuitry in the circuit cards, this waste heat must be removed. To remove this waste heat, ambient air is typically blown through the spaces, or slots, between circuit cards. As the cards become more closely arranged, minimizing the distance between connections and maximizing the number of circuit cards in a given footprint, it becomes increasing difficult to adequately cool sets of cards arranged across a single backplane.
Several different card arrangements have been developed to minimize the distance between cards and maximize economy of space while providing adequate cooling of the circuitry. In one arrangement, interface cards are arranged on two separate backplanes. The two backplanes are then interconnected by switch fabric cards connected to both backplanes. However, this design requires very precise alignment of the switch fabric cards and backplanes within a rack, or housing. This is difficult to achieve and even a small misalignment can result in damage to the electrical interface pins connecting the switch fabric cards to the backplanes. In addition, the use of an additional backplane substantially increases the cost of this configuration.
Another possible arrangement disposes the interface cards on one side of the backplane while placing the switch fabric cards on an opposite side of the backplane. This arrangement minimizes the distance between the card connections, but suffers from poor economy of space and requires access to both sides of the rack. The additional space required to accommodate cards extending out from both sides of the backplane makes this design impractical for interconnecting several platforms.
Both of the above described arrangements also pose substantial challenges to adequate cooling of the closely spaced cards. Often, the ambient air used to cool the circuit cards is passed sequentially over two or more sets of cards. The first set of cards often transfers so much heat to the cooling air that subsequent sets of cards are not sufficiently cooled.
The methods of supplying ambient air to sets of circuit cards also present challenges. Cooling fans often create turbulent airflow on the downstream side of the fan. In a platform that has a high circuit card density, the turbulent airflow often results in unequal flow rates through the slots formed between the cards. In order to assure adequate airflow through each slot, larger or more fans are sometimes used in the device even though the total airflow is theoretically sufficient to cool each component of the device. One alternative is to use ducting to direct airflow to each slot. Another is to use baffles to limit airflow in slots that would otherwise receive more airflow than necessary in order to force the flow to other slots.
Each of these techniques has disadvantages. Larger or extra fans take up additional space, are more expensive and consume excess power. Baffles increase cost and the overall pressure in the system, and may require use of larger or more fans than otherwise theoretically necessary. Thus, current techniques for directing airflow often result in electronic device designs resulting in an inefficient use of power, space and/or production resources.
Therefore, what is needed is a system and method that provides efficient cooling capability in a telecommunications equipment rack that supports a high density circuit card arrangement.